A hydraulic percussion device often needs a pressure accumulator in order to even out pressure variations which arise from when the percussion device is in use. Pressure accumulators constitute a pressure-tight space, which is divided into at least two separate smaller spaces, for example by means of a pressure-tight membrane. A predetermined gas pressure is applied to a first side of the membrane. The pressurized gas may for example be nitrogen or some other suitable gas. A pressurized fluid that drives the membrane forwards may be provided on the second side of the membrane, which means that the pressure medium (the pressurized gas) on the first side of the membrane will be compressed. The pressure accumulator at the same time stores energy that can be released when required to provide pressurized fluid to a desired destination. In this way a certain volume of pressurized fluid may be stored in the accumulator.
Normally an accumulator is placed at the side of a hydraulic percussion device, above a hydraulic percussion device, i.e. axially behind the percussion device's impact piston chamber. A disadvantage with such solutions is that the part of the accumulator that projects out from the rest of the percussion device is exposed to impacts and to environmental effects. Such solutions also make the percussion device harder to handle. Furthermore, if a pressure accumulator is provided on an extension of a percussion device, the total length of the percussion device will be longer, which is of course a disadvantage for its use.
European patent number EP 0 947 293 discloses a device in connection to a hydraulic fluid driven percussion device, which percussion device comprises at least a frame and an impact piston. The impact piston is arranged to carry out a reciprocating motion caused by the pressure from the pressurized fluid, and further means to feed pressurized fluid to, and away from the percussion device, and a pressure accumulator in communication with the impact piston's pressurized fluid space. The pressure accumulator is along its entire length substantially formed as a ring-shaped space that surrounds the impact piston, by mounting a separate bushing around the frame which has a ring-shaped cavity. The ring-shaped space around the impact piston is arranged to be divided into two pressure chambers that are separated from one another by a bushing-like elastic membrane, whereby the first pressure chamber is intended to be filled with a compressible pressurized medium, and the second pressure chamber is in fluid communication with some pressurized fluid space of the impact piston via at least one channel that extends in the percussion device's radial direction. The frame's periphery is provided with a first ring-shaped cavity to form the first pressure chamber and the bushing is, in a corresponding way, provided with a second ring-shaped cavity to form the second pressure chamber. The bushing-like membrane is arranged between the frame and the bushing.
A disadvantage with the accumulator that is described in European patent number EP 0 947 293 is that if one wants to achieve a higher initial charging pressure in the accumulator, it has to contain a lot of small channels that extend in the radial direction, and the holes at the end of each channel have to be sufficiently small so that the membrane will not be driven into the holes and break when the accumulator is in use. The membrane can namely be subjected to large stresses and deformations, which means that the membrane material can have an unnecessarily short lifetime. Such a device can therefore be complex and time consuming to manufacture, and when the membrane contained therein breaks, there will be a stop in operation, which creates extra work and costs.
Another problem with the solution above is that the pressure accumulator that works in a radial direction can increase the total width of the percussion device, which can be a disadvantage when using a percussion device that has to be moved or used along and/or inside a narrow channel/a narrow hole, such as a percussion drilling machine.